substSlice(ConstList args,
int[] index)Enabled: @return A single list of a single Astro, whose functor is based on
literal functor info of this qterm, and whose args are the
concatentation of the substSlice of the qargs of this qterm.

index - Further indexes after a hole's hole-num. For example,
If a dollar-hole's hole-num is 3 and index is [4,5], then
the dollar-hole would access args[3][4][5]. Similarly,
an at-hole with hole-num 3 would store into
bindings[3][4][5].